A light communication system may include a light transmitter to transmit data bits in modulated light packets to a light receiver, such as a camera. The light packets modulated to convey the data bits at a transmit bit rate. A logic level of each transmitted data bit may be represented as light that is intensity modulated to indicate the logic level. The camera samples the received light packets once every camera frame at a frame rate of the camera, to produce light samples at the frame rate. The data bits may then be demodulated based on the light samples.
Ideally, the transmit bit rate and the camera frame rate (or sample rate) are synchronized so as to produce consistent, error free samples that result in correctly demodulated bits in the receiver. In practice, however, the transmit bit rate and the camera frame rate are not often synchronized because the transmitter and the receiver operate based on their respective different clocks that are not synchronous with each other, i.e., their clocks are asynchronous. When the transmit bit rate and the frame rate are not synchronized, then the transmitted data bits slowly “slip” through or “drift” by the camera frames or sample times. Due to this drift, occasionally camera sample times will coincide with and thereby sample edge transitions in the intensity modulated light, which results in an indeterminate sample, i.e., a sample that has an indeterminate level. Disadvantageously, this may result in an erroneous demodulated data bit.
In the drawings, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.